Chemical sensor with conductive cup-shaped sensor surface

ABSTRACT

A system includes a sensor including a sensor pad and a well wall structure defining a well operatively coupled to the sensor pad. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. The system further includes a conductive layer disposed over the lower surface and the wall surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/260,818 filed Apr. 24, 2014, which is a continuation of U.S. patent application Ser. No. 13/354,108 filed Jan. 19, 2012, the entire contents of which are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

This disclosure, in general, relates to sensor arrays and methods for making same.

BACKGROUND

Electronic sensor arrays are finding increased use for detecting analytes in fluids, such as gases or liquids. In particular, arrays of sensors based on field effect transistors are finding use in detecting ionic components, such as various cations, anions or pH. Such sensors are often referred to as ion-sensitive field effect transistors or ISFETs.

Recently, such sensor arrays have found use in sequencing polynucleotides. Nucleotide addition results in the release of ionic species that influence the pH in a local environment. Sensors of the sensor arrays are used to detect changes in pH in the local environment resulting from the nucleotide addition. However, the pH of the local environment can be influenced by the interaction of various materials with hydrogen ions, leading to lower accuracy and less sensitivity to changes caused by nucleotide addition.

As such, an improved sensor array would be desirable.

SUMMARY

In a first aspect, a system includes a sensor including a sensor pad and a well wall structure defining a well operatively coupled to the sensor pad. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. A conductive layer is disposed over the lower surface and at least a portion of the wall surface.

In a second aspect, a system includes an array of sensors, each sensor of the array of sensors including a sensor pad and a well wall structure defining a plurality of wells. Each well is operatively coupled to an associated sensor pad. Each well is further defined by a lower surface disposed over the associated sensor pad. The well wall structure defines an upper surface and defines, for each well, a wall surface extending between the upper surface and the lower surface. In association with a well of the plurality of wells, a conductive layer is disposed over the lower surface and at least a portion of the wall surface.

In a third aspect, a method of forming a sensor system includes forming a well wall structure defining a well operatively coupled to a sensor pad of a sensor. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. The method further includes depositing a conductive layer over the well wall structure. The conductive layer overlies the upper surface, wall surface and lower surface. The method also includes planarizing to remove the conductive layer from the upper surface.

In a fourth aspect, a method of sequencing a polynucleotide includes depositing a polynucleotide conjugated polymeric particle in a well of a system. The system includes a sensor including a sensor pad and a well wall structure defining a well operatively coupled to the sensor pad. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. The system further includes a conductive layer disposed over the lower surface and at least a portion of the wall surface. The method further includes applying a solution including a nucleotide to the well and observing the sensor to detect nucleotide incorporation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1 includes an illustration of an exemplary system including a sensor array.

FIG. 2 includes an illustration of an exemplary sensor and associated well.

FIG. 3 and FIG. 4 include illustrations of an exemplary well structure.

FIG. 5 includes an illustration of an exemplary array of wells within a well structure.

FIG. 6 includes cross-sectional illustrations of exemplary well configurations.

FIG. 7 through FIG. 11 include illustrations of exemplary work pieces during exemplary manufacturing processes.

The use of the same reference symbols in different drawings indicates similar or identical items.

DETAILED DESCRIPTION

In an exemplary embodiment, a system includes a sensor having a sensor pad and a well wall structure defining a well operatively coupled to the sensor pad. The well includes a lower surface disposed over the sensor pad and includes a wall surface defined by the well wall structure. A conductive layer is disposed over the lower surface and at least a portion of the wall surface. The conductive layer can be formed of a metal or a conductive ceramic. Optionally, a passivation layer is disposed over the conductive layer. The passivation layer can include a material having a high intrinsic buffer capacity.

In another exemplary embodiment, a system can be formed by a method including forming a well wall structure over a sensor including a sensor pad. The well wall structure defines a well operatively coupled to the sensor pad. The well has a lower surface disposed over the sensor pad and a wall surface formed by the well wall structure. The well wall structure also defines an upper surface. The method further includes depositing a conductive layer over the well wall structure and planarizing the conductive layer to remove the conductive layer from the upper surface. Optionally, the method can further include depositing a passivation layer over the conductive layer.

In a particular embodiment, a sequencing system includes a flow cell in which a sensory array is disposed, includes communication circuitry in electronic communication with the sensory array, and includes containers and fluid controls in fluidic communication with the flow cell. In an example, FIG. 1 illustrates an expanded and cross-sectional view of a flow cell 100 and illustrates a portion of a flow chamber 106. A reagent flow 108 flows across a surface of a microwell array 102, in which the reagent flow 108 flows over the open ends of microwells of the microwell array 102. The microwell array 102 and a sensor array 105 together may form an integrated unit forming a lower wall (or floor) of flow cell 100. A reference electrode 104 may be fluidly coupled to flow chamber 106. Further, a flow cell cover 130 encapsulates flow chamber 106 to contain reagent flow 108 within a confined region.

FIG. 2 illustrates an expanded view of a microwell 201 and a sensor 214, as illustrated at 110 of FIG. 1. The volume, shape, aspect ratio (such as base width-to-well depth ratio), and other dimensional characteristics of the microwells may be selected based on the nature of the reaction taking place, as well as the reagents, byproducts, or labeling techniques (if any) that are employed. The sensor 214 can be a chemical field-effect transistor (chemFET), more specifically an ion-sensitive FET (ISFET), with a floating gate 218 having a sensor plate 220 optionally separated from the microwell interior by a passivation layer 216. In addition, a conductive layer (not illustrated) can be disposed over the sensor plate 220. The sensor 214 can be responsive to (and generate an output signal related to) the amount of a charge 224 present on passivation layer 216 opposite the sensor plate 220. Changes in the charge 224 can cause changes in a current between a source 221 and a drain 222 of the chemFET. In turn, the chemFET can be used directly to provide a current-based output signal or indirectly with additional circuitry to provide a voltage-based output signal. Reactants, wash solutions, and other reagents may move in and out of the microwells by a diffusion mechanism 240.

In an embodiment, reactions carried out in the microwell 201 can be analytical reactions to identify or determine characteristics or properties of an analyte of interest. Such reactions can generate directly or indirectly byproducts that affect the amount of charge adjacent to the sensor plate 220. If such byproducts are produced in small amounts or rapidly decay or react with other constituents, multiple copies of the same analyte may be analyzed in the microwell 201 at the same time in order to increase the output signal generated. In an embodiment, multiple copies of an analyte may be attached to a solid phase support 212, either before or after deposition into the microwell 201. The solid phase support 212 may be microparticles, nanoparticles, beads, solid or porous comprising gels, or the like. For simplicity and ease of explanation, solid phase support 212 is also referred herein as a particle. For a nucleic acid analyte, multiple, connected copies may be made by rolling circle amplification (RCA), exponential RCA, or like techniques, to produce an amplicon without the need of a solid support.

In a particular example, FIG. 3 illustrates a system 300 including a well wall structure 302 defining wells 304. The wells 304 are in operative connection with sensor pads 306 of sensors. In particular, a lower surface 308 of the well 304 is defined over at least a portion of the sensor pad 306. The well wall structure 302 defines an upper surface 310 and defines a wall surface 312 extending between the upper surface 310 and the lower surface 308.

The well wall structure 302 can be formed of one or more layers of material. In an example, the well wall structure 302 can have a thickness (t) extending from the lower surface 308 to the upper surface 310 in a range of 0.3 micrometers to 10 micrometers, such as a range of 0.5 micrometers to 6 micrometers. The wells 304 can have a characteristic diameter, defined as the square root of 4 times the cross-sectional area (A) divided by Pi (e.g., sqrt(4*A/π), of not greater than 5 micrometers, such as not greater than 3.5 micrometers, not greater than 2.0 micrometers, not greater than 1.6 micrometers, not greater than 1.0 micrometers, not greater than 0.8 micrometers or even not greater than 0.6 micrometers.

The system can further include a conductive structure 314 disposed over the sensor pad 306 and at least partially extending along the well wall. For example, the conductive structure 314 can extend at least 40% along the wall surface 312, such as at least 50%, at least 65%, at least 75%, or even at least 85% along the wall surface 312. The upper surface 310 of the well wall structure 302 can be free of the conductive structure 314.

The conductive structure 314 can be formed of a conductive material. For example, the conductive material can have a volume resistivity of not greater than 6.0×10⁷ ohm-m at 25° C. In particular, the volume resistivity can be not greater than 1.0×10⁷ ohm-m at 25° C., such as not greater than 5.0×10⁶ ohm-m, or not greater than 2.0×10⁶ ohm-m at 25° C. The conductive material can be a metallic material or alloy thereof, or can be a ceramic material, or a combination thereof. An exemplary metallic material includes aluminum, copper, nickel, titanium, silver, gold, platinum, or a combination thereof. In particular, the metal can include copper. In another example, the ceramic material can include titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof. In particular, the titanium oxynitride is a high nitrogen content titanium oxynitride. Further, the titanium aluminum nitride can be a low aluminum content titanium aluminum nitride.

Optionally, a passivation structure 316 can be disposed over the conductive structure 314 and optionally the upper surface 310 of the well wall structure 302. In particular, the passivation structure 316 can have a high intrinsic buffer capacity. For example, the passivation structure 316 can have an intrinsic buffer capacity of at least 2×10¹⁷ groups/m². Intrinsic buffer capacity is defined as the surface density of hydroxyl groups on a surface of a material measured at a pH of 7. For example, the passivation structure 316 can have an intrinsic buffer capacity of at least 4×10¹⁷ groups/m², such as at least 8×10¹⁷ groups/m², at least ×10¹⁸ groups/m², or even at least 2×10¹⁸ groups/m². In an example, the passivation structure 316 has an intrinsic buffer capacity of not greater than 1×10²¹ groups/m².

In particular, the passivation structure 316 can include an inorganic material, such as a ceramic material. For example, a ceramic material can include an oxide of aluminum, hafnium, tantalum, zirconium, or any combination thereof. In an example, the ceramic material can include an oxide of tantalum. In another example, the ceramic material includes an oxide of zirconium. In a further example, the upper surface 310 can be coated with a pH buffering coating. An exemplary pH buffering coating can include a functional group, such as phosphate, phosphonate, catechol, nitrocatechol, boronate, phenylboronate, imidazole, silanol, another pH-sensing group, or a combination thereof.

In an example, the passivation structure 316 can have a thickness in a range of 5 nm to 100 nm, such as a range of 10 nm to 70 nm, a range of 15 nm to 65 nm, or even a range of 20 nm to 50 nm.

While FIG. 3 illustrates a single-layer well wall structure 302, a single-layer conductive structure 314 and a single-layer passivation structure 316, the system can include, one or more well wall structure layers, one or more conductive layers or one or more passivation layers. For example, as illustrated in FIG. 4, a well wall structure 402 defines wells 404 positioned over sensor pads 406. The well wall structure 402 can be formed of one or more layers 420, 422, or 424. In the example illustrated in FIG. 4, a layer 420 of the well wall structure 402 can include an oxide of silicon or TEOS. A layer 422 can include a nitride of silicon, and a layer 424 can include an oxide of silicon or TEOS.

The well wall structure 402 defines wells 404 having a lower surface 408 and upper surface 410. A wall surface 412 is defined between the lower surface 408 and the upper surface 410. A conductive structure 414 in contact with the sensor pad 406 can extend across the lower surface 408 of the well 404 and at least partially along a wall surface 412 of the well 404. For example, the conductive structure 414 can extend at least 40% along the wall surface 412, such as at least 50%, at least 65%, at least 75%, or even at least 85% along the wall surface 412. While illustrated as a single layer, the conductive structure 412 can include one or more layers, such as one or more metal layers or one or more ceramic layers.

The conductive structure 414 can be formed of a conductive material. For example, the conductive material can have a volume resistivity of not greater than 6.0×10⁷ ohm-m at 25° C. In particular, the volume resistivity can be not greater than 1.0×10⁷ ohm-m at 25° C., such as not greater than 5.0×10⁶ ohm-m, or not greater than 2.0×10⁶ ohm-m at 25° C. The conductive material can be a metallic material or alloy thereof, or can be a ceramic material, or a combination thereof. An exemplary metallic material includes aluminum, copper, nickel, titanium, silver, gold, platinum, or a combination thereof. In particular, the metal can include copper. In another example, the ceramic material can include titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof. In particular, the titanium oxynitride is a high nitrogen content titanium oxynitride. Further, the titanium aluminum nitride can be a low aluminum content titanium aluminum nitride.

Optionally, one or more passivation layers 416 or 418 can be disposed over the well wall structure 402 and conductive structure 414. In the illustrated example, the passivation layers 416 or 418 are disposed over the well wall structure 402 and conductive structure 414 including an upper surface 410 of the well wall structure 402. In an example, the passivation layer 416 can include aluminum oxide and the passivation layer 418 can include tantalum oxide. Alternatively, one or more additional layers formed of one or more additional materials, such as aluminum oxide, tantalum oxide, or zirconium oxide, can be formed as part of a passivation structure over the conductive structure 414 and the well wall structure 402. In a particular example, the passivation layer 418 defining an outer surface has an intrinsic buffer capacity of at least 2.0×10¹⁷ groups/m². Intrinsic buffer capacity is defined as the surface density of hydroxyl groups on the surface of material measure at a pH of 7. For example, the passivation layer 418 can have an intrinsic buffer capacity of at least 4×10¹⁷ groups/m², such as at least 8×10¹⁷ groups/m², at least 1×10¹⁸ groups/m², or even at least 2×10¹⁸ groups/m². In an example, the passivation layer 418 has an intrinsic buffer capacity of not greater than 1×10²¹ groups/m².

In a further example, the passivation layer 418 can be coated with a pH buffering coating. An exemplary pH buffering coating can include a functional group, such as phosphate, phosphonate, catechol, nitrocatechol, boronate, phenylboronate, imidazole, silanol, another pH-sensing group, or a combination thereof.

In a particular example illustrated in FIG. 5, a system 500 includes a well wall structure 502 defining an array of wells 504 disposed over or operatively coupled to sensor pads of a sensor array. The well wall structure 502 defines an upper surface 506. A lower surface 508 associated with the well is disposed over a sensor pad of the sensor array. The well wall structure 502 defines a sidewall 510 between the upper surface 506 and the lower surface 508. As described above, a conductive structure in contact with sensor pads of the sensor array can extend along the lower surface 508 of a well of the array of wells 504 and along at least a portion of the wall 510 defined by the well wall structure 502. The upper surface 506 can be free of the conductive structure.

While the wall surface 312 of FIG. 3 and wall surface 412 of FIG. 4 is illustrated as extending substantially vertically and outwardly, the wall surface can extend in various directions and have various shapes. Substantially vertically denotes extending in a direction having a component that is normal to the surface defined by the sensor pad. For example, as illustrated in FIG. 6, a well wall 602 can extend vertically, being parallel to a normal component 612 of a surface 614 defined by a sensor pad. In another example, the wall surface 604 extends substantially vertically, in an outward direction away from the sensor pad, providing a larger opening to the well than the area of the lower surface of the well. As illustrated in FIG. 6, the wall surface 604 extends in a direction having a vertical component parallel to the normal component 612 of the surface 614. In an alternative example, a wall surface 606 extends substantially vertically in an inward direction, providing an opening area that is smaller than an area of the lower surface of the well. The wall surface 606 extends in a direction having a component parallel to the normal component 612 of the surface 614.

While the surfaces 602, 604, or 606 are illustrated by straight lines, some semiconductor or CMOS manufacturing processes can result in structures having nonlinear shapes. In particular, wall surfaces, such as wall surface 608 and upper surfaces, such as upper surface 610, can be arcuate in shape or take various nonlinear forms. While the structures and devices illustrated herewith are depicted as having linear layers, surfaces, or shapes, actual layers, surfaces, or shapes resulting from semiconductor processing may differ to some degree, possibly including nonlinear and arcuate variations of the illustrated embodiment.

Such structures as illustrated in FIG. 3 or FIG. 4 can be formed by depositing a conductive material over the well wall structure and sensor pads, planarizing or etching the conductive material, and optionally depositing a passivation material over the conductive material and the well wall structure. As illustrated in FIG. 7, a portion 702 of a system proximal to a sensor array is illustrated, and a portion 704 of the system proximal to electrical contacts is illustrated. One or more layers 708, 710 or 712 can be deposited over a CMOS structure 706, sensor pads 714 and contact pad 716. In an example, one or more layers of an oxide of silicon, a nitride of silicon, or TEOS can be deposited to overlie the sensor pad 714 and contact pad 716. In the illustrated example, a layer 708 of silicon oxide or TEOS is deposited over the CMOS structure 706. A layer 710 of silicon nitride is deposited over the layer 708, and a layer 712 of silicon oxide or TEOS is deposited over the layer 710. The total thickness of the one or more layers 708, 710 or 712 can be in a range of 0.3 μm to 10 μm, such as a range of 0.5 μm to 6 μm.

As illustrated in FIG. 8, the layers 708, 710, or 712 can be etched to define a well 818 and a well wall structure defined by the remainder of the layer 708, 710, or 712. In an example, the wells 818 can be exposed using a wet etch, a plasma etch, or combination thereof. In particular, a fluorinated plasma etch process can be utilized to expose the sensor pads 714. As illustrated in FIG. 8, the layers can be masked to prevent exposure of the conductive pads 716.

As illustrated in FIG. 9, a conductive layer 920 can be deposited over a lower surface of the well 818 and along at least a portion of the sidewall defined by the layers 708, 710, or 712. For example, the conductive layer 920 can be deposited using sputtering, atomic layer deposition, or a liquid deposition technique. The conductive layer 920 can be planarized to remove the conductive material from an upper surface of the well wall structure defined by the layers 708, 710, or 712. In an example, the conductive layer 920 can be formed of a metal, a ceramic, or combination thereof. An exemplary metal includes aluminum, copper, nickel, titanium, silver, gold, platinum, or a combination thereof. In particular, the metal can include copper. In another example, the ceramic material can include titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof. In particular, the titanium oxynitride is a high nitrogen content titanium oxynitride. Further, the titanium aluminum nitride can be a low aluminum content titanium aluminum nitride. The conductive material can have a volume resistivity of not greater than 6.0×10⁷ ohm-m at 25° C. In particular, the volume resistivity can be not greater than 1.0×10⁷ ohm-m at 25° C., such as not greater than 5.0×10⁶ ohm-m, or not greater than 2.0×10⁶ ohm-m at 25° C.

Optionally, one or more passivation layers can be deposited over the conductive layer 920. For example, as illustrated in FIG. 10, a passivation layer 1022 can be deposited over the conductive layer 920 and the well wall structure defined by layers 708, 710 or 712. An optional passivation layer 1022 can be formed of a ceramic material, such as an oxide of aluminum, hafnium, tantalum, zirconium, or any combination thereof. In particular, the passivation layer 1022 can include aluminum oxide, tantalum oxide, or combination thereof. In a particular example, the passivation layer 1022 can include zirconium oxide. In an example, the passivation layer has a high intrinsic buffer capacity such as an intrinsic buffer capacity of at least 2.0×10¹⁷ groups/m². For example, the passivation layer 1022 can have an intrinsic buffer capacity of at least 4×10¹⁷ groups/m², such as at least ×10¹⁷ groups/m², at least 1×10¹⁸ groups/m², or even at least 2×10¹⁸ groups/m². In an example, the passivation layer 1022 has an intrinsic buffer capacity of not greater than 1×10²¹ groups/m².

Following formation of the conductive layer 920 and optional passivation layer 1022, the contact pad 716 can be exposed. For example, the wells 818 and well wall structure in proximity to the sensor pads 714 can be masked and an access 1124 can be formed to expose the contact pad 716. For example, the contact pad 716 can be exposed using a wet etch, a plasma etch, or combination thereof. In particular, a fluorinated plasma etch process can be utilized to form access 1124 that terminates at the contact pad 716. In a particular example, the access 1124 can be filled with a conductive material to provide an electrical connection to the contact pad 716.

In a first aspect, a system includes a sensor including a sensor pad and a well wall structure defining a well operatively coupled to the sensor pad. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. A conductive layer is disposed over the lower surface and at least a portion of the wall surface.

In an example of the first aspect, the upper surface is free of the conductive layer.

In another example of the first aspect or the above examples, the system further includes a passivation layer disposed over the conductive layer over the lower surface and the wall surface. For example, the passivation layer can be disposed over the upper surface of the well wall structure. In an example, the passivation layer includes an oxide of aluminum, tantalum, hafnium, zirconium, or a combination thereof. In an additional example, the system further includes a coating disposed over the passivation layer. For example, the coating can include a functional group selected from a group consisting of phosphate, phosphonate, catechol, nitrocatechol, boronate, phenylboronate, imidazole, silanol, another pH-sensing group, and a combination thereof.

In a further example of the first aspect or the above examples, the conductive layer is formed of a material having a volume resistivity of not greater than 6.0×10⁷ ohm-m at 25° C. For example, the volume resistivity is not greater than 1.0×10⁷ ohm-m at 25° C., such as not greater than 5.0×10⁶ ohm-m at 25° C. or not greater than 2.0×10⁶ ohm-m at 25° C.

In an additional example of the first aspect or the above examples, the conductive layer includes a metallic material. For example, the metallic material is copper, aluminum, titanium, gold, silver, platinum, or a combination thereof. In another example, the conductive layer includes a ceramic material. For example, the ceramic material is titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof.

In a second aspect, a system includes an array of sensors, each sensor of the array of sensors including a sensor pad and a well wall structure defining a plurality of wells. Each well is operatively coupled to an associated sensor pad. Each well is further defined by a lower surface disposed over the associated sensor pad. The well wall structure defines an upper surface and defines, for each well, a wall surface extending between the upper surface and the lower surface. In association with a well of the plurality of wells, a conductive layer is disposed over the lower surface and at least a portion of the wall surface.

In an example of the second aspect, the upper surface is free of the conductive layer.

In another example of the second aspect or the above examples, the system further include a passivation layer disposed over the conductive layer over the lower surface and the wall surface. In an example, the passivation layer is disposed over the upper surface of the well wall structure. In an additional example, the passivation layer includes an oxide of aluminum, tantalum, hafnium, zirconium, or a combination thereof.

In a further example of the second aspect or the above example, the conductive layer is formed of a material having a volume resistivity of not greater than 6.0×10⁷ ohm-m at 25° C. For example, the volume resistivity is not greater than 1.0×10⁷ ohm-m at 25° C., such as not greater than 5.0×10⁶ ohm-m at 25° C., or not greater than 2.0×10⁶ ohm-m at 25° C.

In an additional example of the second aspect or the above example, the conductive layer includes a metallic material. For example, the metallic material includes copper, aluminum, titanium, gold, silver, platinum, or a combination thereof.

In another example of the second aspect or the above example, the conductive layer includes a ceramic material. For example, the ceramic material is titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof.

In a third aspect, a method of forming a sensor system includes forming a well wall structure defining a well operatively coupled to a sensor pad of a sensor. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. The method further includes depositing a conductive layer over the well wall structure. The conductive layer overlies the upper surface, wall surface and lower surface. The method also includes planarizing to remove the conductive layer from the upper surface.

In an example of the third aspect, the conductive layer is formed of a material having a volume resistivity of not greater than 6.0×10⁷ ohm-m at 25° C. For example, the volume resistivity is not greater than 1.0×10⁷ ohm-m at 25° C., not greater than 5.0×10⁶ ohm-m at 25° C., or not greater than 2.0×10⁶ ohm-m at 25° C.

In another example of the third aspect or the above examples, the conductive layer includes a metallic material. For example, the metallic material is copper, aluminum, titanium, gold, silver, platinum, or a combination thereof.

In an additional example of the third aspect or the above examples, the conductive layer includes a ceramic material. For example, the ceramic material is titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof.

In a further example of the third aspect or the above examples, the method further includes forming a passivation layer over the planarized conductive layer. For example, the passivation layer includes an oxide of aluminum, tantalum, hafnium, zirconium, or a combination thereof.

In another example of the third aspect or the above examples, the method further includes depositing a coating over the passivation layer.

In a fourth aspect, a method of sequencing a polynucleotide includes depositing a polynucleotide conjugated polymeric particle in a well of a system. The system includes a sensor including a sensor pad and a well wall structure defining a well operatively coupled to the sensor pad. The well is further defined by a lower surface disposed over the sensor pad. The well wall structure defines an upper surface and defines a wall surface extending between the upper surface and the lower surface. The system further includes a conductive layer disposed over the lower surface and at least a portion of the wall surface. The method further includes applying a solution including a nucleotide to the well and observing the sensor to detect nucleotide incorporation.

In an example of the fourth aspect, the polymeric particle includes multiple copies of the polynucleotide, and a change in ionic concentration results from incorporation of the nucleotide with the polynucleotide. The change in ionic concentration changes an electrical characteristic of the sensor indicative of the nucleotide incorporation.

As used herein, the terms “over” or “overlie” refers to a position away from a surface relative to a normal direction from the surface. The terms “over” or “overlie” are intended to permit intervening layers or direct contact with an underlying layer. As described above, layers that are disposed over or overlie another layer can be in direct contact with the identified layer or can include intervening layers.

Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed.

In the foregoing specification, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and FIG.s are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, the use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.

After reading the specification, skilled artisans will appreciate that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, references to values stated in ranges include each and every value within that range. cm What is claimed is: 

1. A system comprising: a sensor including a sensor pad; a well wall structure defining a well operatively coupled to the sensor pad, the well further defined by a lower surface disposed over the sensor pad, the well wall structure defining an upper surface and defining a wall surface extending between the upper surface and the lower surface; a conductive layer disposed over the lower surface and extending incompletely up the wall surface; and a layer disposed over the conductive layer over the lower surface and the wall surface, the layer including an oxide of aluminum, tantalum, hafnium, zirconium, or a combination thereof.
 2. The system of claim 1, wherein the upper surface is free of the conductive layer.
 3. The system of claim 1, wherein the layer is further disposed over the upper surface of the well wall structure.
 4. The system of claim 1, further comprising a coating disposed over the layer.
 5. The system of claim 4, wherein the coating includes a functional group selected from a group consisting of phosphate, phosphonate, catechol, nitrocatechol, boronate, phenylboronate, imidazole, silanol, another pH-sensing group, and a combination thereof.
 6. The system of claim 1, wherein the conductive layer is formed of a material having a volume resistivity of not greater than 6.0×10̂7 ohm-m at 25° C.
 7. The system of claim 6, wherein the volume resistivity is not greater than 1.0×10̂7 ohm-m at 25° C.
 8. The system of claim 7, wherein the volume resistivity is not greater than 5.0×10̂6 ohm-m at 25° C.
 9. The system of claim 8, wherein the volume resistivity is not greater than 2.0×10̂6 ohm-m at 25° C.
 10. The system of claim 1, wherein the conductive layer includes a metallic material.
 11. The system of claim 10, wherein the metallic material is copper, aluminum, titanium, gold, silver, platinum, or a combination thereof.
 12. The system of claim 1, wherein the conductive layer includes a ceramic layer.
 13. The system of claim 12, wherein the ceramic material is titanium nitride, titanium aluminum nitride, titanium oxynitride, or a combination thereof.
 14. A method of forming a sensor system, the method comprising: forming a well wall structure defining a well operatively coupled to a sensor pad of a sensor, the well further defined by a lower surface disposed over the sensor pad, the well wall structure defining an upper surface and defining a wall surface extending between the upper surface and the lower surface; forming a conductive layer over the lower surface and extending incompletely up the wall surface; and forming a layer disposed over the conductive layer over the lower surface and the wall surface, the layer including an oxide of aluminum, tantalum, hafnium, zirconium, or a combination thereof.
 15. The system of claim 14, wherein the conductive layer is formed of a material having a volume resistivity of not greater than 6.0×10̂7 ohm-m at 25° C.
 16. The system of claim 15, wherein the volume resistivity is not greater than 1.0×107 ohm-m at 25° C.
 17. The system of claim 16, wherein the volume resistivity is not greater than 5.0×106 ohm-m at 25° C.
 18. The system of claim 17, wherein the volume resistivity is not greater than 2.0×106 ohm-m at 25° C.
 19. The system of claim 14, wherein the conductive layer includes a metallic material.
 20. The system of claim 19, wherein the metallic material is copper, aluminum, titanium, gold, silver, platinum, or a combination thereof. 